<!DOCTYPE html>
<html >
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>选择器</title>
   <style>
       h1,h2{
           color: blue;
       }
       div.title{
           color: brown;
       }


   </style>
</head>
<body>
        <h1>一号标题</h1>
        <h2>二号标题</h2>
        <h3>三号标题</h3>
        <h4>四号标题</h4>
        <h5>五号标题</h5>
        <h6>六号标题</h6>
        
        <div>内容一</div>
        <div>内容二</div>
        <div class="title">内容三</div>
        <p  class="title">内容四</p>
        <p>内容五</p>
        <p>内容六</p>


</body>
</html>